How can we be certain about anything?
On the one hand, there must be and always is de facto certainty - not least because it is impossible to doubt everything, and in practice we doubt one thing in terms of other certainties.
But this still leaves open the question - how can we be certain about anything?
In particular, how can someone be certain about religion or a 'philosophy of life'; in particular, how can someone be certain enough that they will be strong and solid about Christianity in the way that people clearly were in the past.
The certainty of past Christians tends to be set aside as naive, fanatical or due to insufficient knowledge; but that is to beg the question - which is to assume precisely that which needs to be proved.
The problem with answering this question is that we use the wrong model of certainty.
The typical model of certainty which is wheeled-out is that of science; usually some solid bit of science like the periodic table or Newton/ Einstein's laws.
But this is a false example, because scientists are not certain about science in the overwhelming and personal way which is being sought in relation to religion.
Scientists regard the current truth as a working hypothesis; but any scientist worth his salt would be prepared to re-conceptualize their present understanding if or when something better came along - as Newtonian Physics was re-conceptualized by Relativity and Quantum Theory.
Another false model of certainty is philosophy: specifically the idea that really good and 'rigorous' philosophy would lead to certainty (and serve as a foundation for other forms of knowledge).
But this is wrong, too, since the history of philosophy is the history of disagreements about what is certain.
Philosophy resembles a battleground more than it resembles a set of solid foundations!
So what should be the model of certainty?
The answer is love - and a good specific instance is a child's certainty that he loves his Mother and his Mother loves him.
Now, if we acknowledge that a child knowing for certain that his Mother loves him is a valid example of certainty, and that therefore the proper answer to the question of how to be certain is related to love more than to science or philosophy, then it can be seen that certainty is a matter of the heart rather than 'the head', or the intellect.
So, for a Christian to be certain of the truth of Christianity, or something more specific like the divine inspiration of the Bible, or the validity of the ten commandments - is a matter of love: specifically certainly of the love of Jesus Christ and our Heavenly Father, and certainty of love for Them.
Thus it is that the simplest Christians are typically the most certain; because simple Christians are generally those (such as children) whose faith is based on a conviction of God's love and in love of God.
And intellectual Christians are typically, chronically, intrinsically plagued by doubts.
Because their belief is based upon intellectual assent, and intellectual assent is not the kind of thing susceptible to certainty.
This has implications for 'evidence' in relation to belief.
A child who knows his Mother's love is not open to empirical persuasion on the matter; it is not something which can either be proven or disproven.
Of course, a child's confidence can be broken. He may become ill, damaged, brainwashed, demoralized, alienated...
And indeed modern Man has been by thus broken by secularism, as the way of destroying certainty in the love of God.
However, it can be seen that although successful, the consequence is not simply to destroy one specific certainty, in the love of God, but to destroy the capacity for all certainty, and to damage the capacity for parental and filial love.
And a life view, a philosophy, a religion is properly built from certainty: such that one certainty leads to another; and then certainties become mutually reinforcing - and we become situated, based and rooted in reality in the way that (lacking it) we crave.
What are the legitimate grounds for the reality of this internal certainty. We need to be certain, and we want to know that of which we are certain - how to go about it?
If it is a matter of the heart, then it is to the heart we should look: we need to examine our hearts to discover that of which we are certain - and to recognize and acknowledge that as being validated in the only way that certainty can be validated - and to start with that.
Assuming that Christianity is real and true - than all certainties of the heart - of whatever kind and on whatever subject - will, eventually, lead to Christ.